Load balancing in routers

Mon Apr 8 16:03:40 UTC 2002

On 8 Apr 2002, Paul Vixie wrote:

> > I seem to remember fast switching was per-destination, and CEF was
> > round robin. But it seems CEF is now per-destination as well in IOS 12.2.
> > Round robin is optional.

> CEF is flow-hashed, and the hash seems to include both source and
> destination, and seems to include the port numbers.  This is by observing
> the behaviour of flows hitting various members of the F.ROOT-SERVERS.NET
> set, each of whom sends F's address to several upstream routers using OSPF.
> CEF works like a charm -- the load is never split by more than 45-55 and
> that's damn good for wire speed hashing in my view.

> We used CEF in 11.x and it behaved the same way.  It was never round-robin
> in any way we could observe.

You're right. I was thinking of process switching.

According to:
http://www.ils.unc.edu/dempsey/186s00/reorderingpaper.pdf

packet reordering at MAE East was extremely common a few years ago. Does
anyone have information whether this is still happening?